In the operation of a commercial coal slurry transportation pipeline, plugging or blocking of the pipeline due to the build-up of coal particles in the interface between the coal slurry and a carrier fluid, such as water, has been avoided by the use of a pseudo fluid immediately in advance of and immediately behind the batches of coal slurry being transported through the pipeline by the carrier fluid. The formation and use of this pseudo fluid has been described in U.S. Pat. No. 2,920,923. Such pseudo fluid is comprised of a suspension of coal fines or particles of small size (in the range of 90 to 100% of the solids passing a 325 mesh Tyler standard screen). This pseudo fluid possesses the properties of a fluid having a greater density and/or viscosity than the slurry. The pseudo fluid at the front of a batch of coal slurry is called a cap. The pseudo fluid at the rear of the batch of coal slurry is called a tail.
The purpose of the cap and tail pseudo fluid is to exert a suspending force on the relatively coarse coal particles in the interface between the coal slurry batch and carrier fluid if the cap and tail were not present. This suspending force supplied by the caps and tails is equal to or greater than the suspending force exerted by the slurry by itself on such course coal particles.
U.S. Pat. No. 3,690,732 is also pertinent to the making of a cap from a coal slurry batch for the foregoing purpose. This patent discloses the way in which a cap can be created from the slurry itself to facilitate the pumping of the slurry and decreases the overall cost of operation of the slurry pipeline.
In the operation of certain commercial coal slurry pipelines, such as a 1500-mile coal slurry pipeline, from Wyoming to Arkansas, it is proposed that the pipeline will pass near locations at which coal-using plants are located. It is desirable, therefore, to use the pipeline to supply a portion of the coal slurry being used by each of these plants, whereby a single pipeline will provide the source of fuel for a number of plants at different locations.
In the first few years of pipeline system operations, the quantity of coal which will be transported through the pipeline generally will not be sufficient to keep the pipeline full of coal slurry at all times. Accordingly, coal will be transported as a slurry in batches, and the batches of coal slurry will be spaced apart by batches of a carrier fluid, such as water. To avoid the plugging of the pipeline as mentioned in U.S. Pat. No. 2,920,923, caps and tails must be provided at the front and rear ends of all of the batches of coal slurry in the pipeline.
U.S. Pat. No. 2,920,923 discloses that the pseudo fluid defining a cap and a tail is formed by grinding coal into fines or fine particles at the entry point of the pipeline. Each batch of coal slurry as pumped into the pipeline has a cap and a tail of fine coal slurry added to the batch. However, this patent does not teach or suggest that the pseudo fluid formed at the entrance station can be re-used as caps and tails at the downstream delivery points along the pipeline if the batch of coal slurry is removed from the pipeline for any reason.
Where a single pipeline is to furnish coal in batches to several plants along the pipeline, it may be necessary that all of the coal slurry be removed from the pipeline at each coal delivery point to obtain stable pipeline operation and balance different flow rates in each section of the pipe-line. The portion of the slurry required at the delivery point will be dewatered to form a coal cake for use at the corresponding plant. This creates the problem of forming the cap and tail required for the remaining portions of the coal slurry batches when the remaining coal slurry batches are returned to the pipeline for movement to the next downstream delivery point. Because of this problem, a need has arisen for improvements in the method for producing caps and tails material at each of the downstream delivery points where coal is removed from the pipeline. This invention will permit the movement of a coal slurry batches with caps and tails requirements at each delivery point as now would be done using existing art.